I'm skeptical because you are so willing to get "proof" he has cancer. "I'll post a picture of him!" "I'll get a video of him saying he has cancer!" Like is this a loving joke? He supposedly has one year to live and you are going to make him admit it, you are going to make your father say on video that he has cancer to show a bunch of random people on the internet. What the forget is wrong with you?
If my dad was dying I would not give a stuff what anyone said. I wouldn't post a video of him saying it to an online forum. I don't even think I'd be able to hold the camera to record it without breaking down.
If this is actually real it is tragic, and your father has my sympathy. But you are a terrible person. You need to stop caring what random people on the forum think and start caring about your father enough to not put him through stupid stuff like that.
And if you are lying about something like this, shame on you. Because that would be absolutely vile.